Ubiquiti - Open Systems Interconnection (OSI) Model скачать в хорошем качестве

Ubiquiti - Open Systems Interconnection (OSI) Model

The Open Systems Interconnection (OSI) Model is a 7-Layer data model that very simply describes the software protocols and hardware involved in end-to-end network Communication. At the top of the OSI stack, the Application Layer represents protocols such HTTP for web browsing. End-users interface their Internet Apps at this layer, and unlike Network Admins, are generally not concerned with the lower layers. A Payload passing down the OSI stack undergoes Encapsulation, process whereby each layer adds specific information to help move the payload across the network, closer to its final destination. After passing from Layer-7, Layer-6 & Layer-5, the Payload arrives at Layer-4, the Transport Layer, where it is encapsulated with Network Protocol & Port information. The resulting envelope of encapsulated data is called, a Segment. At Layer-3, the Network Layer, the Segment becomes encapsulated with IP Address information. The resulting envelope of encapsulated data is called, a Packet. At Layer-2, the Data Link Layer, the Packet becomes encapsulated with MAC Address information. The resulting envelope of encapsulated data is called, a Frame. Finally, at Layer-1, the Physical Layer, the Frame is converted to a modulated Carrier Signal, then transmitted over a physical medium, be it wired (via copper & fiber lines), or wirelessly (via radios). Across the Network, APs, Switches, and Routers help move the Payload to its intended destination, examining info Layer-by-Layer in a process called, Decapsulation. Here, the AP listens to a Host’s Wirelessly signal to rebuild the Encapsulated Data, then determines at Layer-2, the intended local recipient is the Gateway, and forwards along a rebuilt Frame via Ethernet. Similarly, the Gateway receives the wired, transmitted signal, rebuilds the Encapsulated Data, determines at Layer-2 that it is the intended recipient, but discovers that the Layer-3 address belongs to a host on a different network segment, and forwards along a rebuilt Frame via Ethernet. The process is repeated until the Payload reaches a Network host, who at Layer-3, discovers that it is the intended recipient, and at Layer-4, that an established connection exists for the Packet, so the End-user can retrieve the Payload in the respective Application at Layer-7. At Layer-2, data moves between Nodes according to MAC addresses. This is commonly understood as Intranetwork communication, like when a Host communicates over a Ubiquiti AP and/or Switch to reach another Host, but also, when data moves across direct links, like two Peered Internet Routers linked at datacenter. At Layer-3, data moves between Network Hosts according to IP addresses. Commonly understood as Internetwork communication, this includes Ubiquiti Routers that move data between networks. At Layer-3, data moves between Network Hosts according to IP addresses. And at Layer-4, protocol and port assignment helps hosts decide how to establish the connection, if necessary, on both sides. As a final networking note—the term “Packet” broadly describes any Network Traffic, even when discussing the Layer-1 ‘Physical Signal’, Layer-2 ‘Frame’, Layer-4 ‘Datagram’, or Layer-7 ‘Data Payload’.